A typical industrial gas turbine engine has multiple combustion chambers in a circular array about the engine shaft in a “can annular” configuration. A respective array of transition ducts, also known as transition pieces, connects the outflow of each combustor to the turbine inlet. Each transition piece is a tubular structure that channels the combustion gas flow between a combustion chamber and the turbine section.
The interface between the combustion system and the turbine section occurs between the exit end of each transition piece and the inlet of the turbine. One or more turbine vanes mounted between outer and inner curved platforms is called a nozzle. Retainer rings retain a set of nozzles in a circular array for each stage of the turbine. Upper and lower seals on an exit frame of each transition piece seal against respective outer and inner retainer rings of the first stage nozzles to reduce leakage between the combustion and turbine sections of the engine. These seals conventionally have sufficient clearance in their slots to accommodate relative dynamic motion and differential thermal expansion between the exit frame and the retainer ring. For this reason, such seals may be called “floating seals”. However, such clearance increases gas leakage across the seal, thereby reducing engine efficiency.